SPHERICAL LENS

A lens with a surface that has the form of part of a sphere, i.e a constant radius.

While a spherical lens surface is much easier to grind and polish than an ASPHERICAL lens, such lenses are inherently optically imperfect because all spherical lenses manifest spherical aberration whereby light is refracted more at the edge of the lens than it is at the centre.

This causes light passing through the edges of a spherical lens to focus on a different plane to light passing through the middle, the effect increasing the further off-axis the light-path. For this reason in lens design only a central portion of the full radius of spherical elements are generally utilised.